The present invention relates to the removal of water from hydrocarbonaceous solids. More specifically, the present invention relates to a heat efficient method for the removal of water from hydrocarbonaceous solids, such as peat, containing large amounts of moisture. The present invention also relates to a heat efficient method to remove water from a hydrocarbonaceous solid such as peat prior to the conversion of the solid to a more valuable product such as a synthetic gaseous and liquid fuel.
Certain hydrocarbonaceous solids, particularly lower rank coals such as lignite and peat contain appreciable amounts of moisture. For example, peat can contain up to about 80-90% by weight water. This large amount of water must be removed, at least in part, if the peat is to serve as an efficient heat source by direct combustion or to serve as a feed to a high temperature process for converting the peat to a more valuable fuel, e.g. to convert the peat by gasification to a fuel gas. Moisture removal is required in each of these instances since much of the potential heating value of the peat would otherwise be consumed in the evaporation of the water from the peat at the high temperatures encountered. For example, when the peat is burned directly, much of the heat generated must be used to evaporate the water originally present in the peat. As a result, the full heating value of the peat is not achieved. Similarly, if the peat is to be subjected to a high temperature gasification reaction, the water present is evaporated during the reaction thus necessitating large, additional amounts of heat to sustain the reaction. Clearly, these disadvantages cannot be overcome by merely removing the water from the peat by heating and evaporation steps since the same inefficiencies are present.
The prior art has recognized the importance of removing water from hydrocarbonaceous solids. In Lamb, U.S. Pat. No. 3,327,402, coal fines are dried at low temperatures by contacting the fines with a volatile low molecular weight solvent such as acetone or various alcohols in which water is highly soluble at ambient temperatures to remove the water from the coal fines. The coal fines, in turn, are subjected to heating to evaporate the volatile solvent and to provide a relatively dry product. Similarly, in Murphy, U.S. Pat. No. 4,014,104, water is removed from lignite by contact with a low boiling organic solvent miscible in water. The solvent and remaining water is then removed from the lignite by heat. Characteristic of the Lamb and Murphy processes is the utilization of solvents in which water is highly soluble, such as alcohols. These alcohol solvents are expensive, volatile and cannot be efficiently used as medium to transfer the dried solids, as a slurry, to a high temperature reaction vessel to convert the solids to more valuable products. Further, separation of the alcohol, for reuse, from the extracted water by distillation requires the utilization of significant amounts of expensive energy.
The prior art has also removed moisture from a coal having a high moisture contact by contacting the coal with a heated, high boiling oil or oil slurry to evaporate the moisture contained in the coal. See for example, U.S. Pat. Nos. 3,520,067; 3,599,885 and 3,953,927. Contacting hydrocarbonaceous materials with liquids as part of a processing sequence is also illustrated in U.S. Pat. Nos. 1,863,669 (bitumen extraction with benzene); 1,881,968; 2,610,115 and 3,552,031 (water removal). In general, these latter prior art methods, where water removal is the express goal of the process, require the use of heat to remove the water from the solids by evaporation and are, as a result, thermally inefficient.